{ 
    const obj = {
        a: 1,
        b: "two",
        [Symbol("c")]: true as any
    };

    type keys = keyof typeof obj;
    
    // symbol值
    const key: keys = Symbol('id');
    const key1: keys = 'a';
    const key2: keys = 'b';
    // 错误示例
    const key3: keys = 'q';

    /**
     * keyof T：可能会含于symbol类型
     */
}